Pre-press color proofing is a procedure used by the printing industry for creating representative images of printed material without the high cost and time required to actually produce printing plates and set up a high-speed, high-volume, printing press to produce a single example of an intended image for customer approval. The intended image may require several corrections and may need to be reproduced several times to satisfy customers requirements. Using prepress color proofing rather than producing printing plates saves time and money.
Commonly assigned U.S. Pat. No. 5,268,708 describes an image processing apparatus having half-tone color proofing capabilities. An intended image is formed on a sheet of thermal print media by transferring dye from a sheet of dye donor material to the thermal print media by applying thermal energy to the dye donor material. This image processing apparatus 10 is shown in FIG. 1 and is comprised of a media carousel 100; lathe bed scanning subsystem, which includes laser printhead 500; vacuum imaging drum 300; and thermal print media and dye donor material exit transports.
The operation of the image processing apparatus comprises metering a length of the thermal print media from roll 34 on carousel 100. The thermal print media is cut into sheets, transported to the vacuum imaging drum, registered, wrapped around, and secured on the vacuum imaging drum. A length of dye donor material from another roll, also on carousel 100, is metered out of the media carousel, and cut into sheets. The dye donor material is transported to and wrapped around the vacuum imaging drum, such that it is superposed in the registration with the thermal print media.
After the dye donor material is secured to the periphery of the vacuum imaging drum, the scanning subsystem writes an image on the thermal print media by focusing laser energy on the dye donor material as the thermal print media and the dye donor material on the spinning vacuum imaging drum are rotated past the printhead. A translation drive traverses the printhead axially along the vacuum imaging drum in coordinated motion with the rotating vacuum imaging drum to produce the intended image on the thermal print media.
The dye donor material is removed from the vacuum imaging drum and a second sheet of dye donor material, of a different color, is wrapped around the vacuum imaging drum in registration with the thermal print media. The imaging process is repeated with dye from the second color dye donor material being added to the intended image on the thermal print media. Additional sheets of dye donor material are processed in a similar fashion to create the intended. Once the thermal print media with the intended image leaves the exit tray it is transported to a lamination apparatus which uses heat and or pressure to transfer the image formed on the thermal print media to a paper selected by the customer.
Although the present process is satisfactory, it is not without drawbacks. The cost of a color proof from the image processing apparatus described is relatively high. For example, a different color dye donor material is needed for each color added to the thermal print media. Thus, a media carousel is required, which contains rolls of the different color dye donor material. This adds expense to the image processing apparatus. The image processing apparatus is also complicated because each different color sheet of dye donor material must be in precise registration with the thermal print media on the vacuum imaging drum. The process is time consuming because an intended image must be printed three or four times using different dye donor material to the thermal print media. Also, the vacuum drum speed is decreased each time a sheet is loaded on or removed from the drum.
One alternative to using dye donor material for color proofing is to use an ink jet to form an intended image on the media. A problem with conventional ink jet images is that the inks are in contact with the media which allows them to migrate into the media, which causes a density shift.